1. Field of the Invention
This invention relates to a control system of a communication network, and, in particular, to a control system of a local area network (LAN).
2. Description of the Prior Art
Typical prior art communication network control systems include (a) CSMA base-band LAN, (b) broad-band LAN, and (c) TDMA base-band LAN in combination with digital PBX. The prior art also includes U.S. Pat. No. 4,516,272, "COMMUNICATION NETWORK", issued to the present applicant on May 7, 1985 and assigned to the assignee of this application, which is hereby incorporated by reference, Japanese Patent Laid-open Publication No. 57-104339, "OPTICAL COMMUNICATION NETWORK", invented by the present applicant and assigned to the assignee of this application, and Japanese patent application No. 58-139543, "COMMUNICATION NETWORK", invented by the present applicant and assigned to the assignee of this application. See, also, commonly assigned U.S. Pat. No. 4,707,828 and the prior art cited therein.
The above-mentioned (a) CSMA base-band LAN is suitable for the application in which packets are relatively short and transmitted sporadically as in the case of transmitting data information and textual information. However, in the case where a packet to be transmitted is of indefinite length, a packet is produced continuously, and/or real time processing is required, as in the case of a multi-media communication, the rate of collisions rises and this tends to inhibit high throughput. What is meant by multi-media communication in the field of LAN is that information to be transmitted includes not only data and text, but also image, voice and video in combination. The above-described (b) broad-band LAN is difficult to apply to multi-media communication and it also has problems in cost and ability to expand. Although the above-described (c) TDMA (time division multiplex access) base-band LAN in combination with digital PBX is technically most suitable among the prior art for application in the field of multi-media communication, it still suffers from the problems in cost and limited ability to expand. In particular, when it is applied to multi-media communication, the cost can be prohibitive.
The prior inventions described in my above-mentioned prior patent and applications are most suitable for application in the field of multi-media communication in many respects. For example, the basic features of my earlier inventions commonly include (1) first-come-first-served logic, (2) multi-coupling structure, and (3) multi-input-single-output function. In a communication network having these features, when two or more signals are input into a single node of the network, the node allows only the first signal to pass therethrough based on the (1) first-come-first-served logic and (3) multi-input-single-output principle, though the node is connected to more than two other nodes or terminals according to the (2) multi-coupling concept.
In my prior inventions, a particular communication route must first be established prior to transmission of information. For this purpose, a source terminal having information to send first sends a call packet into the network constructed by a plurality of nodes interconnected according to the multi-coupling concept. The call packet is disseminated into the network as passing through nodes, and, upon receipt of this call packet by a destination terminal, a call-back packet is returned to the source terminal again passing through various nodes, thereby establishing a particular communication route between the source and destination terminals. In this manner, a packet must pass through a number of nodes, and, thus, a preamble or leading section of the packet is lost slightly every time when the packet passes through a node, thereby causing a propagation delay. This is disadvantageous because it takes longer to establish a particular transmission route, which, in turn, increases the rate of occurrence of packet collision.
In my prior communication networks, a plurality of transmission routes may be simultaneously established. However, since each node has the multi-input-single-output function, such a plurality of transmission routes to be established at the same time cannot have common nodes. In other words, in my prior networks, a plurality of simultaneously established transmission routes cannot extend crossing each other. This can be a limitation in increasing the use rate of a network system.